Influence of biochar particle size on biomethane production from glucose

The particle size of biochar affects the degradation of biomass during anaerobic digestion. This study investigated the influence of particle sizes (>2.0, 2.0–1.0, 1.0–0.5, 0.5–0.25, 0.25–0.15, 0.15–0.063, and <0.063 mm) of wheat straw biochar (BC), synthesized at 900 °C for 1 h on the biomethane potential (BMP) of glucose under mesophilic condition (37 °C). The results show that course biochars enhanced the biomethane potential of glucose compared to fine-sized ones. The significant breakthrough found was that the reactors doped with a particle size of 1.0–0.5 mm (BC0.5) had the highest cumulative BMP of 247.64 mL·[g-volatile solid (VS)] −1 followed by > 2.0 and 2.0–1.0 mm (231.45 and 222.40 mL (g VS) −1 , respectively). Adding biochar particles smaller than 0.5 mm resulted in significantly (p < 0.05) lower BMP values. The particle size also influenced the biomethane production constant rate (k), with BC1.0 having the highest k (0.0083 day −1 ) compared to BC < 0.063 (0.0044 day −1 ). The biochars BC > 0.5 had higher volatile solids (8.18 %) than smaller ones. SEM-EDX analysis revealed that BC0.5 exhibits trace elements (Co, Mn, Ni, and Fe) of equal proportions distributed on the surface. The concentrations of heavy metals (Cr, Zn, Pb, Cu, and Cd) are relatively the same among the biochars. Therefore, their inhibitory effect on biomethane production could be neglected. However, BC0.5 also had the highest DFT-specific surface area of 496 m 2 /g, which could result in the improvement of the kinetics of biomethane production. • Biochar supplementation enhanced the biomethane potential of glucose. • The biochar particle size of 0.5–1.0 mm had the highest cumulative biomethane potential. • Particle size 0.5–1.0 mm enhanced the biodegradability of glucose. • The addition of biochar can promote stability within the reactor.